A River Runs to It
An aquarium gurgles gently along the wall of a conference room at the UGA School of Marine Sciences. The sound seeps into the room slowly, humbly, steadily, the way five Georgia rivers empty into the vast Atlantic Ocean.
These rivers once seemed relentlessly endless in their volume. But to some they have begun to look as vulnerable and finite as the water in that aquarium.
Scientists say that, until recently, they knew surprisingly little about the coastal ecology of Georgia, where rivers supply water for drinking, crop irrigation, and pulp and paper mills even for the nourishment of near-coast seafood harvests. In fact, some aspects of the complex interaction of rivers and oceans have perplexed researchers.
"For a long time we thought the rivers came down and dumped water into the ocean and that was the end of it," UGA marine scientist Richard Wiegert said. "Here is this huge ocean. What impact do these rivers have?
"Through their delivery of nutrients, through their delivery of pollutants if they are polluted and through their change in salinity, they really do have an impact," he said. "We recognize that now."
The Georgia coast today remains the least-developed part of the entire Eastern seaboard. These 120 miles of coastline have somehow evaded the extensive development that has overwhelmed South Carolina to the north and Florida to the south. Yet its future has become as murky as its waters.
The beauty and seclusion of the Georgia coast once attracted some of the nation's wealthiest families, from the exclusive Jekyll Island Club of the Rockefellers, Morgans and Vanderbilts to the Carnegie mansion refuge on Cumberland Island. But what was once the playground of the rich is now prime real estate for commercial, recreational and residential development.
"There is going to be tremendous pressure for development on the Georgia coast," Wiegert said. "There has to be good information to guide that development."
The University of Georgia began a three-year, $300,000 study in 1998 funded through the state's Coastal Zone Management program to help provide that information.
The National Science Foundation also has provided $3 million for the Georgia Rivers Land Margin Ecosystem Research (LMER) project. Now in the fifth of six years, LMER is a comparative study of the state's five estuaries, where the waters of river and ocean meet and mix.
Although the two projects are quite different, it is sometimes difficult to tell where one begins and the other ends. The Coastal Zone Management study addresses issues of vital, practical interest to various stakeholders who work and live on the Georgia coast today. LMER is basic scientific research to establish a baseline of data against which to compare the inevitable changes the future will bring.
Research cruises conducted through LMER are in a sense miniature voyages of discovery. Just as Charles Darwin documented a variety of completely unknown or poorly understood scientific phenomena in South America and the Galapagos Islands during the 1830s voyage of the Beagle, UGA researchers do likewise on the research vessel Bluefin along the Georgia coast. They are surveying tiny, sometimes microscopic, plant and animal species and trying to figure out how they interact with each other and their environment.
These studies come at a critical time. In some areas, Georgia's groundwater supply already has been stretched too far. Decisions about the region's future hang in the balance.
"There are certain parts of the coast where saltwater is getting into the water table, so the state has capped water withdrawal," UGA marine scientist Merryl Alber said. "Realistically, that means any new growth, any new water, has to come from someplace besides the groundwater that we've been using for a long time."
One company, The Savannah Group, is looking to the waters of the Ogeechee,
the Savannah and the Altamaha for those additional supplies. The company
has proposed withdrawing water from these rivers, treating it and then
selling it to developers anywhere along the coast. The proposal, which
requires state approval, has provoked a public outcry.
"There are some fishermen on the coast who swear that things have changed in their lifetime," she said. For instance, the fishermen say that wild rice, which requires freshwater, used to grow farther down the coast than it does now.
They also say that in certain docks they now have to scrape barnacles off the hulls where they never had to before. "That suggests that the water has gotten a little saltier in those same ports," Alber said.
Saltier water means problems for Georgia's commercial seafood species. Crabs like what crabbers refer to as sweetwater (low salinity), and the crabbers say there's less sweetwater now than there once was. Oyster distribution along the coast has shifted as well.
"There are a lot of reasons why oyster distribution could have changed on the coast," Alber said. "There are predators that came in. There are diseases that came in with saltwater. But it's possible that the oysters would also change their distribution as a consequence of the salinity."
Changes in agricultural land use, forestry practices or even the weather could affect the salinity of coastal waters, Wiegert said. But until the UGA researchers dredge up more data, the recollections of the watermen will remain unverified.
"The idea is that the land used to retain more water for longer periods of time, so the salinity would go down and stay down for a longer period, but would not go quite as low as it does right now," Wiegert said. "Now we get big peaks. Right after a storm you get very low salinity, but that doesn't last very long. We're trying to get some data on this. Right now there is nothing."
The Georgia Rivers LMER project, on the other hand, has pooled significant amounts of data during the past five years. The goal of the project: to document the transformation and transport of organic and inorganic materials as these rivers pass through the land-sea margin.
This zone extends from the head of the freshwater high tide to the mouth of the estuary a distance that ranges from 26 to 56 miles, depending on the river.
The salinity in this zone ranges from zero in the water coming down the river to about 35 parts per thousand in the water flowing in from the ocean.
"Salt is a conserved material," Wiegert said. "It isn't used as a metabolic product. It isn't broken down or reformed. So if we measure a salinity of 18 parts per thousand, we know that that's the result of a mixture of a certain amount of river water with a certain amount of ocean water."
A river's size and point of origin also affect what the researchers measure in the estuaries. After all, water spends only about a week in the estuaries of bigger, faster-flowing rivers, compared to a month or two in slower rivers. "There's more time in the slower systems to have things happen to the material that comes in with the river water," Alber said.
The researchers expected to see a big difference in the amount of organic material that flows into the estuaries, depending on the geologic characteristics of the individual rivers. The blackwater rivers drain the sandy soils of the coastal plain watersheds. Organic matter passes through sandy soils like Bulldog football star Champ Bailey rushing by a squad of hapless opponents. "That's why you can't grow anything in south Georgia without a lot of fertilizer," Alber said.
The clearwater rivers pass through the coastal plains too, but they originate in the uplands, where stickier clay soil predominates. Indeed, UGA marine scientist Mary Ann Moran found at least twice as much dissolved organic carbon from decaying plants and soil organic matter in the blackwater Satilla than in the clearwater Altamaha. More importantly, Moran discovered that sunlight chemically modifies this dissolved organic matter in ways that tend to make it more easily processed by microbes.
Other measurements yielded only a minor variation where the researchers might have expected to see otherwise. Alber, for example, has measured no significant differences in bacterial production among all five rivers. Also, UGA marine scientist Larry Pomeroy found no significant difference among rivers in respiration the amount of oxygen in a water sample. But he did document a seasonal difference: There was more respiration during the summer months than the winter.
Alber said she suspects that higher rates of bacterial production take place either in the marshes the rivers pass through or in feeder creeks.
"It seems like a lot of processing occurs in those marshes," Alber said. "The water goes into the marsh and when it comes out it's different because of what's happened in the marsh itself."
While the inland marshes appear to influence the estuaries, the Atlantic coast tides do likewise from the sea. Sapelo Island, the geographic center of the Georgia coast, has the highest tides anywhere on the eastern seaboard save New England. The tides get lower both north and south of Sapelo because of the south Atlantic Bight, the section of coastline that curves from northern Florida on up through Georgia and South Carolina.
"It focuses the tidal effect like a big lens," Wiegert said. These high tides, in turn, have a big effect on the estuaries.
Alber has observed one such effect on the ebb and flow of the tides: A line of foam, an accumulation of organic material, often forms where creeks empty into the estuaries. The foam line forms at ebb tide, acting as a dynamic barrier to the mixing of creek and estuarine waters, then dissipates at flood tide.
"It's a small-scale phenomenon, but we think it might be important because it's repeated," Alber said. A similar, larger, longer-lived phenomenon occurs off the coast. "It's where the fish accumulate. It's where the birds go to eat the fish. It's where the fishermen go to catch the fish. We know those fronts are important biologically."
Working with UGA physical oceanographer Changsheng Chen (Research Reporter, Fall 1998), Alber discovered that the foam line on the Ogeechee River coincided with a density front, which is related to the amount of salt in the water. Alber towed a plankton net through the foam line, then identified and counted the different types of organisms she caught. It turned out that species diversity was high, but that bacterial activity was not.
It will take further research to determine exactly what biological role the phenomenon plays in the estuary and whether it helps determine the amount of food in the system. "What's coming out of the creek has different bacterial production rates than what's in the estuary. We certainly see that," Alber said. "If it's true that it's really in the creeks where things are happening more than we realize, that would be a fairly interesting conclusion."
While Alber measures production rates of bacterial populations as a whole, Moran and UGA marine scientist Robert Hodson focus on specific types. Bacteria are by far the most numerous life form on Earth. Marine bacteria play a key ecological role in breaking down dissolved organic matter, including plant and animal remains, to their chemical building blocks. Yet scientists know little about marine bacterial communities because of their difficulty to culture for laboratory study.
The vast majority of bacteria, in fact, are impossible to culture at all using conventional techniques. But Hodson and Moran have developed a molecular technique that enables them to identify bacterial species that would otherwise look exactly alike, even through a microscope.
With a few refinements, Hodson and Moran can even tell if specific genes in the bacteria are active. Moran and post-doctoral associate José Gonzáles have used this technique to identify an abundant group of ecologically important bacteria in Georgia's estuaries that they call "marine alpha." The marine alphas grow in water that's not too salty, not too fresh. In these zones of intermediate salinity, alphas account for up to 30 percent of the bacterial community. And they make their living by degrading humus and lignin, a component of woody plants released in the effluent of Georgia's pulp mills.
Hodson and Moran said they hope to use their molecular technique to document the full range of species and genetic diversity of bacteria in Georgia's estuaries. The genetic diversity is important to establish, Hodson said, because it will reveal whether the bacteria are capable of degrading certain exotic or toxic compounds.
The UGA researchers are racing to amass as much data as they can before development further alters the ecology of the estuaries.
"We are lucky that we've been able to get this LMER study going before any big changes began to affect the systems even more than they already are affected," said Duncan Elkins, a UGA graduate student in ecology.
There's little question that Georgians will need to withdraw some of their coastal river water to meet their development needs. Cities upriver have been doing it for years. But so far they have treated the water and then put it back in. The total water volume in the system has remained relatively unchanged, Wiegert said.
But Georgia has never before seen anything like The Savannah Group's proposal, which would involve withdrawing water from one river, but probably putting it back elsewhere.
"The chances of it going back in the same river are slight," Wiegert said. "The chance of it even going into a riverine estuary may be very small."
The Georgia coast is dotted with lagoonal estuaries, those that have no river flowing into them, Wiegert explained. That means water taken from a river that flows into an estuary may be withdrawn, treated, used for coastal development, then put into a lagoonal estuary that has never received freshwater before.
"You're opening a Pandora's box," he said.
For more information, access http://lmer.marsci.uga.edu/.
Steven N. Koppes, an award-winning writer, is the former UGA assistant director of research communications and associate editor of Research Reporter. He has a bachelor's degree in anthropology and a master's in journalism, and is a science writer at the University of Chicago.